Adifference between two groups in an observational study that can explain why the outcomes were very different between the groups is called what?

A confounding variable

Explanation:

A confounding variable is an element, other than the investigated treatment, that may affect the measured outcome of an assay.

The confounding variable occurs when the association observed derives, at least in part, from differences between groups other than the exposure under study, which affect the risk of presenting the outcome of interest.

trump is very poor. he does not look like a cheeto. he doesn't want to build a wall. (switch out he with trump)